The present invention relates to power systems. More specifically, the present invention relates to a system for managing power from a secondary power source in an elevator system from multiple sources to control power drawn from a primary power source.
The power demands for operating elevators range from highly positive, in which externally generated power (such as from a power utility) is used at a maximal rate, to negative, in which the load in the elevator drives the motor so it produces electricity as a generator. The use of the motor to produce electricity as a generator is commonly called regeneration. In conventional systems, if the regenerated energy is not provided to another component of the elevator system or returned to the utility grid, it is dissipated through a dynamic brake resistor or other load. In this configuration, all demand remains on the power utility to supply power to the elevator system, even during peak power conditions (e.g., when more than one motor starts simultaneously or during periods of high demand). Thus, components of the elevator system that deliver power from the power utility need to be sized to accommodate power demand surges, which may consume a large amount of space in the building. Also, the regenerated energy that is dissipated is not used, thereby decreasing the efficiency of the power system.
In addition, an elevator drive system is typically designed to operate over a specific input voltage range from a primary power supply, such as a utility power source. The components of the drive have voltage and current ratings that allow the drive to continuously operate while the power supply remains within the designated input voltage range. When the utility voltage sags and/or during periods of peak power demand by the drive system components, the elevator system draws more current from the power supply to maintain uniform power to the hoist motor, increasing the overall cost of powering the elevator system. Some conventional systems attempt to alleviate the power demand by connecting a secondary power supply to provide supplemental power to the elevator drive system. However, this does not prevent the elevator drive system from drawing excessive current from the primary power supply, which burdens the components connected to the primary power supply and increases the overall cost of operating the elevator drive system.